The present invention relates generally to instruments for craniomaxillofacial surgery, and more particularly to surgical instruments for mobilizing the bones of the midface in preparation for advancement of the midface with gradual distraction.
Hypoplasia of the midface associated with syndromic craniosynostosis remains a primary challenge to craniomaxillofacial surgeons. Respiration, vision, speech, and esthetics are all affected by impairment of midfacial development. Compromise of function related to midface hypoplasia represents a significant disability. The surgical challenge is to correct the combined skeletal and soft tissue deficiency. Tessier pioneered subcranial and transcranial osteotomies to address the deficiency of craniofacial development. The Le Fort III osteotomy with internal fixation and bone grafting became a standard treatment for these deformities. Despite remarkable improvement in form and function as a result of these procedures, significant deformity often persisted. The magnitude of correction achieved with these procedures often fell short of the ideal anatomical objective. As a result, management of these patients often required repeated procedures to increase the correction. When full correction of the midface was not possible, compensating osteotomies of the maxilla and mandible have been performed to improve the facial balance and dental occlusion. Repeating the procedure or combining it with a Le Fort I maxillary advancement was a common strategy to overcome the limitation in achievable advancement. Even though osteotomies fully separate the midfacial skeleton, the investing soft tissue deficiency limits the effectiveness of conventional osteotomies with intraoperative fragment protraction. Distraction osteogenesis has made it possible to overcome many of the limitations imposed by the deficiency in soft tissue. Distraction can simultaneously enlarge the skeleton and soft tissue. This approach is essential for optimal reconstruction of these disorders.
Even though distraction substantially improves the potential correction of retruded midfaces at the Le Fort III level, the osteotomy and mobilization of the fragment remains a major surgery with significant morbidity. Penetrating the cranial vault during osteotomy, fragment mobilization, or placement of fixation/distraction devices is a known risk. Laceration of the brain by penetration of the cranial vault may result in neurological deficit or death. Intracranial penetration may also occur when reflecting coronal flaps in a field previously treated by forehead advancement. Conventional Le Fort III technique involves complete osteotomy under direct vision followed by fragment mobilization using Kiley-Rowe disimpacting forceps. The purchase of the disimpacting forceps to the Le Fort III fragment is often insecure. The nasal floor contour may not conform to the prongs of the forcep beaks. The oral purchase is on the palate placing the beaks on the mucosa and toward the midline. Transmission of force through the forceps into the Le Fort III fragment is inefficient. Because the efficiency of force generation to mobilize the Le Fort III fragment is poor, a complete osteotomy is essential. Even small areas of incomplete osteotomy will prevent fragment mobilization. Injury to the soft tissue including the eyes and brain may occur if the osteotomy site is over-instrumented. Generating force with the instrument requires counter-traction of the head and is awkward. This is because the vector of force necessary to mobilize the midface with disimpacting forceps is not aligned with the vector of primary resistance.
It would be desirable to provide an improved instrument for mobilizing the Le Fort III midface fragment that alleviates the above-described disadvantages of the Kiley-Rowe disimpacting forceps. Such an improved instrument is provided by the present invention.
In accordance with the present invention, an instrument is provided that is modular and arranged to be assembled in situ. An acrylic splint, preferably custom made for the patient, attaches rigidly to the instrument and positively engages the dental arch of the maxilla. Alternatively, a general use resilient platform may be used to engage the dental arch. Two nasal floor prongs clamp the device in place rigidly. A primary lever extends in the superior-inferior direction in front of the forehead. A secondary lever extends in the medial-lateral direction in from of the dental arch. When mobilization is performed, reciprocal traction is exerted between the forehead and the primary lever. The resultant force on the head and neck is low because the two force vectors are in opposite directions. Torsional force can be exerted via the secondary lever. Controlled force of large magnitude may be exerted on the midface.
Advantages of the present invention include the following. A complete osteotomy is not necessary to obtain a satisfactory mobilization if limited osteotomies in the critical structural buttresses are established. This eliminates the need for complete orbital floor osteotomies and requires limited nasal-frontal osteotomy. Pterygoid plate separation is generally not necessary. Many of the hazardous sites for osteotomy become unnecessary. Transoral access can provide adequate mobilization for major Le Fort III level movements. Protection of the nasal lacrimal system, however, is compromised with limited access. Prophylactic intubation with silicone tubing may be necessary to prevent obstruction of lacrimal drainage. The invention allows for midface mobilization with less bone cutting than with prior art devices and methods. Therefore, the risk of penetrating the cranial vault and injuring the brain is reduced. The orientation of the primary lever in the superior-inferior direction allows reciprocal application of force which decreases the amount of energy needed to stabilize the head during mobilization and reduces the risk of neck injury. The wider stabilization of the device to the dental arch as compared to the middle of the palate with Rowe-Kiley forceps allows greater force to be applied in a torsion manner. This allows mobilization of the zygoma with the midface unit and decreases the risk of an aberrant fracture along the Le Fort II line.
According to one aspect of the present invention, a method of mobilizing the midface bones of a human skull includes the steps of performing a partial osteotomy between the midface bones and the skull and breaking the midface bones free of the skull.
According to another aspect of the present invention, an instrument for mobilizing the midface bones of a human skull includes a grasping member for grasping the midface bones. A lever has a first portion connected in cantilever fashion to the grasping member and has a second portion displaced from the grasping member in a superior-inferior direction relative to the skull. Manually displacing the second portion of the lever in an anterior-posterior direction relative to the skull breaks the midface bones free from the skull.
It is an object of the present invention to provide an improved instrument for effecting mobilization of the midface bones of a skull.
It is a further object of the present invention to provide an improved method of mobilizing the midface bones of a skull.
Other objects and advantages of the present invention will be apparent from the description below of the preferred embodiments and methods for practicing the invention, made with reference to the drawings.